Part Fabrication using Multi-Material Additive Manufacturing

In recent years, the nuclear power industry has been exploring the use of conventional powder metallurgy to fabricate large metal parts for current and next-generation nuclear energy applications. Powder metallurgy has many advantages over other large-scale manufacturing methods (e.g. casting, welding, forging, etc.), which include the fabrication of near-net shape parts with controlled chemistry and improved microstructure in the part. In powder metallurgy processing, parts are manufactured by fabricating complex steel molds in the approximate shape of the part. The mold is then filled with metal powder, sealed and subjected to heat and isostatic pressure, which consolidates the metal powder to a near-net shape part. The geometry of the parts fabricated in this manner is limited by the geometry of the mold and the ability to uniformly fill the complex mold with metal powder. In addition to the engineering cost associated with mold design, there is considerable labor cost with both the fabrication of components and final assembly of the mold. In general, the more geometrically complex the part, the higher the associated cost. Further, with high-customization applications, the tooling costs (i.e. the mold) in lowquantity manufacturing of large-scale parts are significant. Additive manufacturing technology holds the potential to enable low-quantity, highly customized production of metal parts, but state-of-the-art metal 3D printing systems use expensive metal powders and do not have build chambers large enough for energy generation applications. In this Phase I project, a novel multi-material 3D powder printing technology will be used as a digital “front end” to conventional powder metallurgy part fabrication methods. Metal parts will be fabricated by 3D printing metal and supporting powders in inexpensive steel molds and processing the molds using conventional methods used in powder metallurgy. In addition, metal parts will be fabricated by 3D printing the mold, metal, and supporting powders in the same build cartridge. High-temperature processing of this multi-material powder structure results in the in-situ fabrication of a 3D printed mold, which can then be processed using conventional hot isostatic press technology. These manufacturing processes not only allow for the fabrication of geometrically complex parts, they have the potential to significantly reduce tooling costs associated with the engineering and fabrication of conformal steel molds. During the Phase I project, tensile test samples and geometrically complex demonstration samples will be fabricated using these novel digital powder metallurgy manufacturing processes. Commercial applications of this new additive manufacturing process include the fabrication of large-scale customized parts for commercial and federal customers, and the development of a completely new additive manufacturing system that will allow for the fabrication of reproducible, high quality, geometrically complex near-net shaped parts at a reduced cost as compared to conventional low-quantity part manufacturing methods.